1. Field of the Invention
The present invention relates to an automatic internal combustion engine stop device, an internal combustion engine provided with the same and an automatic internal combustion engine stop method; more particularly, to an improvement for optimizing a piston stop position in an automatic internal combustion engine stop device for automatically stopping an internal combustion engine (hereinafter simply referred to as “engine”) during an idling operation thereof, for instance.
2. Description of the Related Art
When a motor vehicle stops at an intersection, for example, to wait for traffic lights to change in the course of running in an urban area, etc., the engine is left idling, which wastes fuel. In view of this, what is called an “idling stop control” has been conventionally performed to stop an engine by cutting off fuel supply to a combustion chamber (by conducting a so-called fuel cut) when specific conditions are satisfied, such when the vehicle is stopped (see, e.g., Japanese Patent Application Publication No. JP-A-2002-70699).
When the engine is stopped by the idling stop control (hereinafter, “idling stop state”), if an engine start condition is satisfied, e.g., the brake pedal is released or the shift lever is operated in the case of an auto transmission vehicle and the clutch pedal is depressed in the case of a manual transmission vehicle, the engine is restarted by driving a starter mechanism and transferring the drive power thereof to the engine, namely, by performing a so-called cranking operation.
When the engine is restarted from the idling stop state as described above, it is typical that initial combustion is caused by supplying fuel to a predetermined cylinder (hereinafter referred to as an “initial combustion target cylinder”) and allowing an ignition plug to ignite the fuel, while performing the aforementioned cranking operation.
In the process of restarting the engine, restartability of the engine is greatly influenced by a condition such as which cylinder is selected as the initial combustion target cylinder or the position of a piston in the initial combustion target cylinder when the idling stop was executed (piston stop position).
For instance, if the piston stop position is not proper, a great deal of vibration is generated at the time of restart, thus giving an uncomfortable feeling to a driver and other vehicle occupants, or the time required for an engine to start up is prolonged to such a level as to give a sense of discomfort (what is called a feeling of delayed start) to the driver.
There will now be described a cause of generation of such vibration and a cause of prolongation of the time required for engine start. For the sake of easier understanding, the following description will be made by taking, as an example, a case where fuel is port-injected in a four-cylinder gasoline engine.
In the event that a piston stop position in an initial combustion target cylinder is near bottom dead center of the intake stroke (e.g., the piston is stopped at the 150 degree position in crank angle after top dead center of the intake stroke), the in-cylinder volume is increased and a large quantity of air is present in the cylinder. In the idling stop state, heat is transferred from the cylinder block and the like to the air in the cylinder, thereby keeping the air at an elevated temperature. This is because the engine was in an operating state just before its stoppage. Furthermore, because the intake valve of the cylinder is open during the intake stroke, an in-cylinder pressure is increased up to an atmospheric pressure nearly simultaneously with the engine stop. This also allows the quantity of air in the cylinder to grow larger than an air quantity available during the intake stroke in a typical engine operation process. That is to say, when the piston stop position in the initial combustion target cylinder lies near the bottom dead center of the intake stroke, a large quantity of air having a relatively high temperature exists in the cylinder. If the cylinder proceeds to a compression stroke after fuel supply is completed through the intake stroke, an air-fuel mixture may self-ignite, at which time a great deal of vibration is generated.
If the piston stop position in the initial combustion target cylinder lies near the bottom dead center of a stroke other than the intake stroke (any one of compression, expansion and exhaust strokes), the intake valve is closed and, under the idling stop control noted above, no fuel is supplied into the cylinder to thereby stop the engine. This means that no fuel is present in the cylinder. For this reason, the situation occurs where fuel is not supplied to the cylinder until the next intake stroke. Thus, initial combustion cannot be brought about unless the compression and expansion strokes begin subsequent to the next intake stroke. This prolongs the time required to start the engine.
On the other hand, if the piston stop position in the initial combustion target cylinder is not near bottom dead center, or if the cylinder is in other strokes than the intake stroke (any one of the compression, expansion and exhaust strokes), the situation occurs where fuel is not supplied into the cylinder until the next intake stroke, as in the aforementioned case. Thus, initial combustion cannot be brought about unless the compression and expansion strokes begin subsequent to the next intake stroke. This prolongs the time required to start the engine.
The above are the cause of generation of vibration and the cause of prolongation of the time required to start the engine. In order to avoid such situations, the piston stop position when the idling stop is performed should be appropriately set and the cylinder having the properly set piston stop position selected as the initial combustion target cylinder. For example, the piston stop position may be set near top dead center, and the cylinder being on the intake stroke at the time of idling stop may be chosen as the initial combustion target cylinder.
Such a manner of setting the piston stop position and choosing the initial combustion target cylinder applies to a port-injection engine. In case of an in-cylinder direct injection engine, the proper piston stop position and the initial combustion target cylinder may be set and chosen differently. In other words, inasmuch as the proper piston stop position may vary depending on engine specifications or the like, it is not always desirable that the piston of the cylinder being on the intake stroke at the time of idling stop be placed near the top dead center (the optimized piston stop position in the present invention is not limited thereto).
However, it is not easy to properly set the piston stop position at the time of idling stop. There is described in Japanese Patent Application Publication Nos. JP-A-2005-282434 and JP-A-2005-315202 a technique of adjusting a piston stop position by reversely rotating the crankshaft at the time of idling stop. Japanese Patent Application Publication No. JP-A-2002-39038 describes a device for restricting a piston stop position by use of a stopper.
With the technique disclosed in Japanese Patent Application Publication Nos. JP-A 2005-282434 and JP-A 2005-315202, however, the reverse rotation of the crankshaft may result in some adverse effects. For example, because the camshaft is reversely rotated and auxiliary mechanical components are reversely driven along with the reverse rotation of the crankshaft, it is concerned that the loads acting on individual components become heavier, thus shortening their life span. Further, in the device described in Japanese Patent Application Publication No. JP-A 2002-39038, there is a need to employ the stopper as an additional member for restricting the piston stop position. This increases the number of components and the requires an additional stopper attachment step in assembling the engine.
Thus, the present inventors have investigated an engine control operation by which a piston stop position can be set at a proper position (for example, a piston of a cylinder in an intake stroke can be stopped in the vicinity of a top dead center) when an engine is stopped by an idling stop control, without reversely rotating a crankshaft or using a stopper (e.g., an engine control operation by which. As a result, the following “piston stop position control” has been developed by the present inventors.
More specifically, when an engine load and an engine speed (rpm) are of given constant values, an engine generates a constant level of output energy. Under such conditions, if the ignition operation of an ignition plug is stopped (hereinafter referred to as “ignition cut”) and if fuel injection is cur off (hereinafter referred to as “fuel cut”), a piston is always stopped at a given constant position.
Based on this principle, the present inventors have found that, if the load on the engine at the moment the idling stop control is performed are removed (e.g., by stopping the operation of an air conditioner and/or an alternator) and if the ignition cut and the fuel cut are carried out when the engine speed is a given constant value (a target idle speed in a load-free state, e.g., 650 rpm), the piston will consistently stop at the same position depending on the relationship between the inertial force of rotating movement of the crankshaft and reciprocating movement of the piston and a reaction force (a resistance force such as friction) counteracting the inertial force.
FIG. 9 is a view illustrating changes in the engine speed during the piston stop position control, wherein the X and Y axes represent time and the engine speed, respectively. Under the piston stop position control, an ignition cut and a fuel cut are performed at an idle speed in a load-free state (at an idle speed in a state of no idle-up control accompanying the lead operation, i.e., at an engine speed falling within the range “A” in FIG. 9).
Curve “I” in FIG. 9 represents changes in the engine speed when the ignition cut and the fuel cut have been performed, with an idling stop condition being satisfied in the load-free state. In this case, because the engine speed falls within the range “A” in advance of satisfaction of the idling stop condition, the ignition cut and the fuel cut are executed substantially at the same moment as the idling stop condition is satisfied. The engine stops when time “α” has lapsed after execution of the ignition cut and the fuel cut.
If the ignition cut and the fuel cut are executed in the load-free state as noted above, the engine is always stopped after lapse of time “α”. This means that the piston stop position at the time of idling stop can be properly set at all times by executing the ignition cut and the fuel cut such that the piston stop position after lapse of time “α” becomes proper (e.g., the piston of the cylinder in an intake stroke stops near a top dead center).
In an actual operating state of the engine, however, it is often the case that the engine is operating under a relatively heavy load, e.g., the operation of an air conditioner. If, in this situation, the load is removed upon satisfaction of the idling stop condition, there is a possibility that the engine speed may be sharply increased (the engine may be accelerated) due to the removal of load.
Curve “II” in FIG. 9 represents a case where a sharp increase in the engine speed occurs due to the removal of load by satisfaction of the idling stop condition in a state of an idle-up control accompanying the load operation. In this case, after the engine speed is sharply increased, it is decreased by a feedback control of an idle speed to a target idle speed (an idle speed in a state of no idle-up control accompanying the load operation, i.e., an engine speed falling within the range “A” in FIG. 9). The ignition cut and the fuel cut are executed when the idle speed comes into the range “A”. As is apparent from the curve “II”, in the idling stop control executed after the engine speed is increased sharply, the decrease rate of engine speed per unit time becomes significantly greater. This leaves a possibility that the engine may be stopped within a short period of time (time “β” in FIG. 9) after execution of the ignition cut and the fuel cut. For this reason, the piston stop position at the time of idling stop is deviated from the piston stop position available in case of the curve “I”, thus making it impossible to properly set the piston stop position. Furthermore, because the ignition cut and the fuel cut are not executed until the sharply increased engine speed drops within a predetermined range, i.e., the range “A”, there is a possibility that the time (time “γ” in FIG. 9) required for the engine to stop after satisfaction of the idling stop condition may be prolonged.
Although the afore-mentioned automatic engine stop operation is directed to a case where an engine is automatically stopped by an idling stop control, the same issue may possibly be applied to a case that, in a so-called a “hybrid car” equipped with an engine and an electric motor for running and adapted to run with a drive power of one or both of the engine and the electric motor, the engine is automatically stopped during the running (the running is carried out only with the driving power of the electric motor or a regenerative operation is started). That is, in case the above-noted “piston stop position control” is employed in an automatic engine stop control during a running of the hybrid car, loads such as electric power generation and the like need to be removed at the same moment as satisfaction of an engine stop condition in order to optimize the piston stop position. The removal of load is accompanied by a sharp increase in an engine speed (acceleration of the engine). Similarly to the above-described case, this may possibly result in deviation of the piston stop position or prolongation of the time required for the engine to stop.